308 PALEONTOLOGY OF ILLINOIS. 



agonal surface nearly twice as wide as long. Second 

 radials nearly as large as the first, a little wider than long, 

 and presenting the usual quadrangular form. Third radials 

 tumid, or projecting distinctly beyond the surface of the 

 second and first ; wider than long, larger than the second, 

 and pentagonal or hexagonal in form ; each bearing on its 

 outer sloping sides two series of tumid, stout alternating 

 brachial pieces, directed horizontally outward, and in all 

 but the two posterior rays, forming the base of two stout 

 arms. In the posterior rays, intermediate brachial pieces 

 are intercalated between the others so as to give origin in 

 each of these rays to three arms, thus making twelve arms 

 to the entire series. 



First anal piece about as wide as long, heptagonal in form, 

 with a flat surface entirely included within the concavity 

 of the under side, supporting in the next range three pieces, 

 which are longer than wide, and curve up so as to form a 

 part of the outer wall, but are not included within the 

 concavity of the under surface. Of these the lateral two 

 have a general oval outline, with eight or nine sides and a 

 tumid surface, while the middle one is hexagonal, moder- 

 ately convex, and much narrower at the inner than the 

 outer end. Above these are three other smaller pieces, 

 connecting with the vault. First interradial pieces about 

 once and a-half as long as wide, with nine sides, the inner 

 half being flat and included within the concavity of the 

 lower side, and the outer tumid. Connecting with the 

 outer end of each of these are two elongated narrow pieces 

 in the second range, which are usually tumid at the lower 

 end, and extend up between the brachial pieces, to connect 

 with the vault. Arms unknown. 



Vault composed of irregular, unequal, tumid, larger and 

 smaller pieces. Of the larger, more prominent pieces, one 

 is situated over each ray, and another at the middle; while 

 a series of four or five somewhat smaller pieces immedi- 

 ately surround the anterior and lateral margins of the mid- 



